The present invention pertains to a developing roller incorporated in a developing device, which uses a nonmagnetic one-component developing agent, of an image-forming device that employs an electrophotographic system, such as a copying machine, printer, a facsimile receiver, etc.
Various types of rollers, such as charged rollers and transfer rollers, developing rollers, etc., are placed around the electrostatic latent image carrier, such as a photosensitive body, etc., in image-forming devices that use electrophotographic systems. The developing roller has the role of conveying toner to the electrostatic latent image carrier, such as a photosensitive body, etc., and making the electrostatic latent image visible.
FIG. 1 shows a typical diagram of developing device 1 that uses a nonmagnetic developing system. This developing device is constructed from developing roller 2, toner receptacle 4 that holds toners 3, 3 . . . consisting of nonmagnetic 1-component developing agent, regulating blade 5, and feed roller 6, etc. Above-mentioned developing roller 1 is made by forming conductive elastic layer 8 around conductive shaft 7, which consists of SUS, aluminum alloy, conductive resin, etc., and forming a single or several resin layers 9 around this conductive elastic layer 8. Direct-current voltage or alternating-current voltage is applied between this developing roller and the photosensitive body. Moreover, feed roller 6 is installed in order to facilitate deposition of toner on the surface of the developing roller. Developing treatment by this type of developing device 1 is performed as follows: First, toner is deposited on the roller surface and developing roller 2 thereby charges this toner by contact or by friction. Next, the charged toner is pressed by regulating blade 5 and further uniformly charged as a toner layer of the desired thickness is produced. Moreover, this toner layer is adsorbed by the electrostatic latent image on photosensitive body 10 and the electrostatic image is thereby made visible to form a toner image. This toner image is transferred to recording paper and then the transferred image on the recording paper is fixed by heat or by pressing.
Polyamide resin comprising xe2x80x94NHCOxe2x80x94 bonds and polyurethane resin have often been used for the outermost layer of developing rolls in order to improve the minus charging properties of toners (Japanese Patent Publication (Kokoku) No. 50(1975)-13661). However, there were problems with using these resins as the outermost layer in that there is a reduction in the minus charge of the toner under high-temperature and high-humidity environments and further, there is a problem in that the phenomenon whereby toner is fixed on the roller surface with long-term use (referred to as xe2x80x9ctoner filmingxe2x80x9d below) occurs, preventing the formation of a toner layer, even under ordinary environments.
Therefore, polycarbonate was used as the main component of the outermost layer. As a result, consistent results were obtained in preventing a reduction in the minus charge of the toner under a high-temperature, high-humidity environment. Moreover, in order to prevent toner filming, silicone-modified polycarbonate was also used as the main component of the outermost layer (Japanese Patent Laid-Open No. 9(1997)-244392). However, since the silicone content of the outermost layer is high and hardness of the outermost layer is high with developing rollers that use this type of outermost layer, there is a problem in that the outermost layer is easily scratched and there is a reduction in durability of the developing roller.
Moreover, there has been a tendency in recent years toward the use of toner with a low melting point of approximately 80xc2x0 C. or lower in order to efficiently fix transferred images on recording paper. When this type of low-melting-point toner is used, not only toner filming, but also fusion of toner on the adjusting blade, occur and a toner layer of the desired thickness is not formed and problems such as image irregularities, etc., readily occur. The above-mentioned problems of toner filming when a low-melting-point toner is used and of fusion of toner on the adjusting blade that are encountered with developing rollers that use polycarbonate or silicone-modified polycarbonate as the main component of the outermost layer have not been successfully conquered
Moreover, there are contact developing systems whereby the surface of the developing roller is brought into contact with photosensitive body and non-contact systems whereby a space is made between this surface and the photosensitive body. Voltage is applied between the photosensitive body and the developing roller with both the contact and the non-contact systems, but it is particularly necessary to apply alternating-current voltage between the photosensitive body and the developing roller by the non-contact contact system because the toner will fly in the above-mentioned space. It is necessary that the developing roller and photosensitive body have a specific contact width (referred to below as the xe2x80x9cnip widthxe2x80x9d) by the contact system. Irregularities in the image will be produced and the image quality will be poor if this nip width fluctuates and therefore, surface hardness of the developing roller must be set at an appropriate range. Moreover, there are problems with the non-contact system in that outer diameter of the roller will change with changes in humidity and changes in temperature and as a result, the space width between the developing roller and photosensitive body will change, leading to irregularities in the image.
In light of the above-mentioned problems, the purpose of the present invention is to prevent a reduction in the charge of the toner under high-temperature, high-humidity environments and prevent toner filming and fusion of toner on the regulating blade. Moreover, the purpose of the present invention is also to prevent fluctuations in nip width and in space width with changes in temperature and changes in humidity.
The first developing roller of the present invention is characterized in that by means of a developing roller that is made by lamination of one or several elastic layers around a conductive shaft and one or several resin layers on said elastic layer, the above-mentioned elastic layer has a JIS A hardness of 50 degrees or less, of the above-mentioned single or several resin layers, at least the outermost layer contains fine particles, and surface roughness of said outermost layer (Rz) is adjusted to within a range of 3 to 15 xcexcm. Furthermore, above-mentioned surface roughness (Rz) is the value in accordance with Japanese Industrial Standard (JIS) B 0601-1994.
The mean particle diameter of the above-mentioned fine particles should be within a range of 5 to 50 xcexcm, particularly 10 to 50 xcexcm.
Moreover, it is preferred that, of the single or several resin layers formed around the elastic layer, at least the outermost layer consist of resin comprising xe2x80x94NHCOxe2x80x94 bonds, for instance, polyamide resin or polyurethane resin. Moreover, this resin composition can comprise repeating units of xe2x80x94ROCO2xe2x80x94, such as polycarbonate. Furthermore, it is further preferred that these resin compositions comprise repeating units of xe2x80x94SiOSixe2x80x94.
And, it is also possible that of the single or several resin layers that are formed around the elastic layer, at least the outermost layer consists of a resin composition comprising acrylic-vinyl acetate copolymer.
Moreover, urethane or nylon material should be used as the above-mentioned fine particles from the point that the particles impart a negative charge to the toner.
It is preferred that the above-mentioned elastic layer consists of a reaction product of a curable composition whose main components are
(A) polymer comprising at least 1 alkenyl group in its molecules and whose repeating units constructing its main chain consist of mainly oxyalkylene units or saturated hydrocarbon units,
(B) curing agent comprising at least 2 hydrosilyl groups in its molecules,
(C) hydrosilylation catalyst, and
(D) conductivity-imparting agent.
Moreover, the thickness of the outermost layer containing the fine particles should be within a range of 5 to 50 xcexcm.
Moreover, an outermost layer with a tensile elongation in conformance with Japanese Industrial Standards (JIS) K 6251 within a range of 300 to 600% should be used as the above-mentioned outermost layer. It is further preferred that the above-mentioned tensile elongation be adjusted to within a range of 400 to 600%, preferably 500 to 600%.
Moreover, it is preferred that roller resistance before coating the single or several resin layers around the elastic layer be 104xcexa9 or higher, and that the roller resistance after coating said resin layers be within a range of 104 to 1010xcexa9, particularly 105 to 108xcexa9.
Moreover, it is preferred that capacitance before coating the single or several resin layers around the elastic layer (C1) be adjusted to within a range of 0.8 to 20 nF, and that capacitance after coating with said resin layers (C2) be adjusted to within a range of 2.5 nF or less.
The above-mentioned developing roller can be used in combination with any developing device that employs the nonmagnetic contact system.
Next, with respect to the second developing roller of the present invention, by means of a developing roller that is made by laminating a single or several elastic layers around a conductive shaft and then laminating a single or several resin layers on said elastic layer, the above-mentioned elastic layer has a JIS A hardness of 50 degrees or less, and the above-mentioned outermost layer has fine particles protruding from its surface because, of the above-mentioned single or several resin layers, at least the outermost layer contains fine particles. Furthermore, the second developing roller of the present invention is characterized in that when height of the fine particles protruding from the above-mentioned surface is L, toner mean particle diameter is rav, and mean distance between the fine particles that protrude from the above-mentioned surface is Dav, the correlation of ravxe2x89xa6Davxe2x89xa680L is established with respect to the fine particles that satisfy the correlation rav/4xe2x89xa6Lxe2x89xa64rav.
In this case, the mean particle diameter rav of the above-mentioned toner should be within a range of 5 to 10 xcexcm.
This type of developing roller can be used in combination with any developing device that employs the nonmagnetic contact system.